Amide compounds have active chemical properties and are involved in various chemical reactions. They are important intermediates in the production of nitriles, amines, etc. and have many industrial uses. For example, acetamide and dimethylformide, which have high dielectric constants, are excellent solvents for many organic and inorganic substances and are widely used in various industries. Acetanilide is an intermediate in the production of sulfonamide medicines, urea is an important raw material for nitrogenous fertilizers and synthetic resins, and caprolactam is the monomer for synthesizing nylon 6.
Most amide compounds are obtained by heating to hydrolyze nitrile compounds in an acidic or basic aqueous solution. However, because amide compounds will continue hydrolyzing to carboxylic acid compounds, the selectivity of this process is not high. Recently, the use of solid acidic materials as a catalyst to solve the drawbacks of the prior art has been extensively discussed and studied, and many catalysts in different forms were successively developed and applied to the selective hydrolysis of nitrile compounds. The catalytic system for use in the hydrolysis of nitrile compounds includes various transition metal catalysts, including copper catalyst [Chem. Soc. Jpn., 44 (1971) 1440] [Bull. Chem. Soc. Jpn., 47 (1974) 1948], palladium catalyst [J. Mol. Catal., 12 (1981) 103], rhodium catalyst [J. Org. Chem., 57 (1992) 2521], platinum catalyst [J. Am. Chem. Soc., 95 (1973) 3030], cobalt catalyst [J. AM. Chem. Soc., 115 (1993) 3618], and nickel catalyst [Bull. Chem. Soc. Jpn., 47 (1974) 1948], which were successively reported to have certain activities when used in the selective hydrolysis of nitrile compounds. However, the aforementioned metal catalysts all cannot be used in industrial processes due to the complex catalytic system and severe reaction conditions.
Currently, manganese dioxide catalyst is the most-reported catalyst for the hydrolysis of nitrile compounds. It has a good catalytic activity for hydrolysis with respect to organic nitrile compounds, of which 6-type manganese dioxide has a higher reaction activity due to its higher surface area [J. Catal., 84 (1983) 267]. The use of manganese dioxide in the hydrolysis of 2-hydroxyisobutyronitrile into α-hydroxyisobutyramide was firstly disclosed in DE 2,131,813. U.S. Pat. No. 4,018,829 discloses the reduction of a heptavalent manganese compound into tetravalent δ-manganese dioxide in a basic environment in a manner of controlling the environmental acidity/basicity, and the use of δ-manganese dioxide as a catalyst for the hydrolysis of 2-hydroxyisobutyronitrile. JP 63-57534 and 63-57535 disclose the use of manganese dioxide in which zinc is incorporated or the use of manganese dioxide obtained by reducing potassium permanganate with a HCl solution, as a catalyst for the hydrolysis of 2-hydroxyisobutyronitrile. It seems that manganese dioxide has been successfully used in the hydrolysis of 2-hydroxyisobutyronitrile and has effectively eliminated the drawbacks of the prior art; however, because the catalytic activity of manganese dioxide is not high, a large amount of catalyst must be used in the process to achieve the desired production of α-hydroxyisobutyramdde. Further, because the reaction activity of manganese dioxide starts to decrease greatly within a very short time, there are also extensive researches and developments on long-life manganese dioxide with high catalytic activity at present. Related researches indicated that the catalytic activity of manganese dioxide is highly related to the preparation method and pretreatment temperature [Bull. Chem. Soc. Jpn., 59 (1986) 2983]. U.S. Pat. No. 4,950,801 discloses that a manganese dioxide catalyst having a large specific surface area, low crystallinity and an amorphous or a nearly amorphous state can be prepared in an acidic environment by introducing at least one kind of Groups IA and IIA metals into manganese dioxide. The modified manganese dioxide catalyst has a higher hydrolysis catalytic activity and a prolonged catalyst life. U.S. Pat. No. 4,987,256 proposes the simultaneous use of manganese (II) and manganese (VII) in a reduction-oxidation reaction to obtain manganese dioxide. The properties of manganese dioxide obtained by this process can be controlled more easily. Also, in the production of manganese dioxide, the sulfates of zirconium, vanadium or zinc are added, whereby the metal zirconium, vanadium or zinc is incorporated into manganese dioxide to improve the activity and life of the catalyst. U.S. Pat. No. 5,087,750 discloses an industrial process for producing α-hydroxyisobutyric acid amide using a fixed bed catalyst in a tubular reactor, which is more suitable for continuous operation, and also proposes that the addition of oxidizing agent in the reactant feed can facilitate prolonging the service lifetime of the manganese dioxide catalyst and increasing the yield of α-hydroxyisobutyric acid amide. U.S. Pat. No. 5,463,123 proposes that the pretreatment of the manganese dioxide catalyst and reducing agent before packing the catalyst in a reactor can suppress the clogging of the by-product oxamide in the catalyst bed during the process, whereby the stability of the catalyst is increased.
Promoting the catalytic activity of manganese dioxide, increasing the stability of the catalyst and prolonging the reaction lifetime of manganese dioxide are key points of the study on modification of the manganese dioxide catalyst. The aforementioned patents all either require using specific preparation processes and/or adding specific promoters to prepare a manganese dioxide catalyst in a specific form, or carrying out a pretreatment of the catalyst before its taking part in the reaction, and adding oxidizing agents during the process, which all result in increasing the complexity of catalyst preparation and reaction operation. In view of the drawbacks of the prior art, the present invention aims to develop a manganese dioxide catalyst that is easily produced, has a high stability and can achieve a commercial level effect within a shorter reaction time.